The present invention relates to a method and apparatus for mixing at least two streams of separately treated tobacco, and more particularly to a method and apparatus for blending first and second types of tobacco (e.g., two different types of tobacco shreds; two different types of tobacco leaves; tobacco shreds and fragments of tobacco ribs, stem and/or birds' eyes; expanded and unexpanded fragments of tobacco ribs; or others) in such a way that the ratio of dry weights of the two tobacco types remains constant irrespective of fluctuations of dry weight of tobacco in successive unit lengths of the one and/or the other stream. Still more particularly, the invention relates to a method and apparatus for automatically blending several tobacco types in such a way that the ratio of dry weights of all tobacco types in the resulting mixture remains constant.
It is well known that many smokers' products (including plain or filter-tipped cigarettes, cigarillos, cigars and cheroots as well as chewing tobacco or sniffing tobacco) contain different types of tobacco. Such different types can be mixed with each other prior or subsequent to comminution of tobacco leaves into shreds and ribs and prior or subsequent to segregation of ribs from tobacco leaf laminae. For example, green tobacco leaves are often destalked and/or their tips removed. The thus removed material is thereupon conditioned separately from the remaining material (laminae). The separately treated portions of green leaves are thereafter mixed with each other, either for the purpose of obtaining the original ratio or to obtain a different ratio of laminae to ribs and/or tips.
The ratio of separately treated tobacco leaf portions in a mixture is particularly important in the manufacture of many types of cigarettes wherein the filler contains shredded tobacco leaf laminae and a certain percentage of comminuted ribs, stem and birds' eyes. The just mentioned ratio is even more important when the separate treatment to which the ribs are subjected independently of shreds includes a puffing or expansion which normally involves impregnating the fragments of ribs with a gaseous or liquid fluid and thereupon rapidly heating the thus impregnated ribs to an elevated temperature at which the outer strata of ribs harden to confine the fluid therein whereby the volume of the thus treated ribs greatly exceeds the original volume.